A warming pause?

The blogosphere (and not only that) has been full of the “global warming is taking a break” meme lately. Although we have discussedthistopicrepeatedly, it is perhaps worthwhile reiterating two key points about the alleged pause here.

(1) This discussion focuses on just a short time period – starting 1998 or later – covering at most 11 years. Even under conditions of anthropogenic global warming (which would contribute a temperature rise of about 0.2 ºC over this period) a flat period or even cooling trend over such a short time span is nothing special and has happened repeatedly before (see 1987-1996). That simply is due to the fact that short-term natural variability has a similar magnitude (i.e. ~0.2 ºC) and can thus compensate for the anthropogenic effects. Of course, the warming trend keeps going up whilst natural variability just oscillates irregularly up and down, so over longer periods the warming trend wins and natural variability cancels out.

(2) It is highly questionable whether this “pause” is even real. It does show up to some extent (no cooling, but reduced 10-year warming trend) in the Hadley Center data, but it does not show in the GISS data, see Figure 1. There, the past ten 10-year trends (i.e. 1990-1999, 1991-2000 and so on) have all been between 0.17 and 0.34 ºC per decade, close to or above the expected anthropogenic trend, with the most recent one (1999-2008) equal to 0.19 ºC per decade – just as predicted by IPCC as response to anthropogenic forcing.

Figure 1. Global temperature according to NASA GISS data since 1980. The red line shows annual data, the larger red square a preliminary value for 2009, based on January-August. The green line shows the 25-year linear trend (0.19 ºC per decade). The blue lines show the two most recent ten-year trends (0.18 ºC per decade for 1998-2007, 0.19 ºC per decade for 1999-2008) and illustrate that these recent decadal trends are entirely consistent with the long-term trend and IPCC predictions. Even the highly “cherry-picked” 11-year period starting with the warm 1998 and ending with the cold 2008 still shows a warming trend of 0.11 ºC per decade (which may surprise some lay people who tend to connect the end points, rather than include all ten data points into a proper trend calculation).

Why do these two surface temperature data sets differ over recent years? We analysed this a while ago here, and the reason is the “hole in the Arctic” in the Hadley data, just where recent warming has been greatest.

Figure 2. The animated graph shows the temperature difference between the two 5-year periods 1999-2003 and 2004-2008. The largest warming has occurred over the Arctic in the past decade and is missing in the Hadley data.

If we want to relate global temperature to global forcings like greenhouse gases, we’d better not have a “hole” in our data set. That’s because global temperature follows a simple planetary heat budget, determined by the balance of what comes in and what goes out. But if data coverage is not really global, the heat budget is not closed. One would have to account for the heat flow across the boundary of the “hole”, i.e. in and out of the Arctic, and the whole thing becomes ill-determined (because we don’t know how much that is). Hence the GISS data are clearly more useful in this respect, and the supposed pause in warming turns out to be just an artifact of the “Arctic hole” in the Hadley data – we don’t even need to refer to natural variability to explain it.

Imagine you want to check whether the balance in your accounts is consistent with your income and spendings – and you find your bank accounts contain less money than you expected, so there is a puzzling shortfall. But then you realise you forgot one of your bank accounts when doing the sums – and voila, that is where the missing money is, so there is no shortfall after all. That missing bank account in the Hadley data is the Arctic – and we’ve shown that this is where the “missing warming” actually is, which is why there is no shortfall in the GISS data, and it is pointless to look for explanations for a warming pause.

It is noteworthy in this context that despite the record low in the brightness of the sun over the past three years (it’s been at its faintest since beginning of satellite measurements in the 1970s), a number of warming records have been broken during this time. March 2008 saw the warmest global land temperature of any March ever recorded in the past 130 years. June and August 2009 saw the warmest land and ocean temperatures in the Southern Hemisphere ever recorded for those months. The global ocean surface temperatures in 2009 broke all previous records for three consecutive months: June, July and August. The years 2007, 2008 and 2009 had the lowest summer Arctic sea ice cover ever recorded, and in 2008 for the first time in living memory the Northwest Passage and the Northeast Passage were simultaneously ice-free. This feat was repeated in 2009. Every single year of this century (2001-2008) has been warmer than all years of the 20th Century except 1998 (which sticks out well above the trend line due to a strong El Niño event).

The bottom line is: the observed warming over the last decade is 100% consistent with the expected anthropogenic warming trend of 0.2 ºC per decade, superimposed with short-term natural variability. It is no different in this respect from the two decades before. And with an El Niño developing in the Pacific right now, we wouldn’t be surprised if more temperature records were to be broken over the coming year or so.

Update: We were told there is a new paper by Simmons et al. in press with JGR that supports our analysis about the Hadley vs GISS trends (sorry, access to subscribers only).

Update: AP has just published an interesting story titled Statisticians reject global cooling, for which they “gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented”.

456 Responses to “A warming pause?”

“Steve, when you select 2002 to present, that range just happens to start with the 2002 unusually warm year, and end with the 2008 low number plus a few months of 2009. You’ve fooled yourself there. Use a longer time span for meaningful global temperature trends.”

Or, better, don’t use the difference between two temperatures.

Use proper grown-up statistics, not what you’d been taught in junior school.

With regard to comment #290 regarding the sub-standard bbc piece by “climate correspondent” Paul Hudson, it would be useful for those who are displeased to communicate your concerns to BBC’s Online editor Jim Todd (jim.todd@bbc.co.uk).

“Response: Land use changes are used in climate models and give a negative forcing (i.e slightly cooling the planet) (Hansen et al, 2005;2007). You were saying?- gavin”

You state Hansen et al 2005; 2007. Could you please provide the full references. I have serious doubts as the veracity of the claim that human land use changes are a negative feedback to the climate system.

[Response: What are your serious doubts based on? The most important impact is clearance of forests for cropland which has an albedo effect (crops are more reflective), roughness effect and impacts evapotranspiration. The Hansen papers are here and here. – gavin]

To Ron Taylor: No. I do not wish the models to fit my “pre-conceived” notions. Not what I said and not what I meant.

To Dhogaza: Wrong as usual on all counts. I stand by my statement on the impacts of land use on climate change. You must understand Sir that climate change is NOT about just warming. It is about CHANGE which can be either warming or cooling. I repeat. I have always argued that it is in land use changes that the greatest human impacts on climate are to be found. No inconsistency here.

Climate change due to land use changes is not just about temperature (e.g. albedo). It is also about changes in precipitation patterns, wind changes and humidity changes due to evapotranspiration among others. I believe the picture is not as simple as using albedo as a primary guide to land use feedback. In fact in my searches, it seems that there is a robust research effort in trying to refine the feedback model of land use change on climate.

329 Rod asks, ” why does the Arctic sea ice extent retreat? Why not stay constant until the thickness all over and all at once reaches zero, and the extent in turn goes to zero like your lake example?”

1. Ocean currents and wind break up the ice, pile it up, and otherwise de-homogenize the ice
2. The Arctic Ocean is big. Weather conditions vary. Solar insolation varies.
3. variations are amplified by salt-rejection. Ice that survives a summer will contain less salt, and so be more resistant to melting.
4. Albedo changes also amplify differences. Open water increases local heating and so local melting.

Your original premise can be restated as, “With no other knowledge except increases or decreases in extent from year to year, our best guess is that volume tends to increase or decrease along with extent, so extent is a reasonable proxy for volume.”

That’s a quite reasonable first-order guess, but it is only a guess, and it is outdated. We have other knowledge now. There is no need to take a stab in the dark. 2008 had less ice than 2007. 2009 may have had less ice than 2008. (Anyone seen any figures yet? ) Are you suggesting we go back to the stab-in-the-dark guess technique instead of using up-to-date volume measurements?

343 Richard S said, “Having said that. Once, just once I would like to see when a new parameter is incorporated into a model, it shows a NOT AS BAD AS WE FEARED outcome. That would make them more believable in a real world.”

About a year ago a study found that the deep permafrost wasn’t likely to melt for a long time (sorry, no cite) Another study earlier this year estimated that Greenland’s ice melt would have a fairly tame upper bound. There’s two examples. I’m sure there are more.

You also noted that none of the scaremongering has come to pass. It seems you’re looking for proof in the form of a passed tipping point. You’ll believe WHEN the Arctic Ocean is ice-free in September. You’ll believe if clathrates and shallow permafrosts start belching more methane than mankind spews carbon dioxide. You’ll believe AFTER all the coral dies. Essentially, you’re looking for the wreckage which won’t exist until after the crash.

Remember, the predictions we’ve heard over the last ten years have been laughable. Ice free Arctic Ocean in 2100?!? 20-40 cm of sea level rise by 2100?!! The reason things always seem to be “worse than they expected” is because most people suck at holistic predictions and scientists tend to be rediculously conservative.

The field is advancing rapidly, so current estimates, using longer and more data sets and better understanding should produce more accurate results. people generally don’t like being proven wrong, so the tendency of bias would be for no change in projections. Either it’s a vast conspiracy to pull an April Fool’s joke on humanity – after all, what else would account for your description (scaremongering) — OR– things are actually worse than they thought.

Land use changes are used in climate models and give a negative forcing

And what’s Richard’s response?

You state Hansen et al 2005; 2007. Could you please provide the full references. I have serious doubts as the veracity of the claim that human land use changes are a negative feedback to the climate system.

Just as predicted.

And then he says:

I stand by my statement on the impacts of land use on climate change. You must understand Sir that climate change is NOT about just warming. It is about CHANGE which can be either warming or cooling. I repeat. I have always argued that it is in land use changes that the greatest human impacts on climate are to be found. No inconsistency here.

Except, of course, just befre you said that you don’t believe land use changes are a negative feedback.

When it comes to science, it doesn’t matter what you think. It doesn’t matter what I think. It only matters where the evidence trail takes us.

If you have some groundbreaking theory, please do present it and get it peer reviewed and let’s see what the scientific community has to say, but if you are not going to do that, then how are you going to support your arrogant hubristic statements? And no, opinions are not support, and you should know better.

RichardC (357), Your four rationales, though, would seem to support my assertion (which started out as a question…) which you paraphrased very well — better than I. Also the general overall trend in the Arctic for the past few decades has been lesser extent and correlated lesser volume/concentration. On the other hand you do see some odd yearly variations and some “strange” regional correlations that run counter to my assertion. So I guess it looks like the standard legal answer: sometimes, yes; sometimes, no! Thanks for your input.

Richard Steckis (343) — A high value for Charney equilibrium climate sensitivity has become less probable due to research conducted since IPCC AR4 appeared. However, a more thorough climate sensitivity, which I believe is called Earth System Sensitivity, has been fairly recently developed. It seems to be a rather alarming 4.5–6 K for 2xCO2.

So the shorter range Charney sensistivy is not as bad, most likely, as some have feared but in the longer term, it gets way too hot, way too hot I fear.

While the total forcing associated with land use is important, it is also important if different uses of land cause different effects on forcing and have occurred at different times. For instance, if deforestation at high latitudes is a particularily strong negative forcing and took place mostly before 1950 and irrigation is a positive forcing and took place mostly after 1950 then it would actually show up as an increase in temperatures although these temperatures may still be at a lower level then they would have been otherwise.

I believe that you have to understand, we did have ice caps all around the poles at one point. When the earth got warmed up, those ice caps melted. What happens to ice when it melts, they cool the surroundings, thus causing what seems to be a paused or “reversed” warming effect. Now will this cooling effect be able to reverse all that humans have done to the earth, I would not know, but for sure that if it does not, once the water warms up to temperature beyond what can be done, you can expect us to go in a GLOBAL WARMING stage. I understand no one knows for sure what’s going on and I am no scientist nor have I done my research, I am just basing this on whatever evidence I see. The fact that we have lost our glaciers are evident in alot of pictures, and if you reason it, those glaciers when melted will give a period of cooling time, but once that cooling stops, you can do the math and tell me what’s suppose to happen?

I stand by my statement on the impacts of land use on climate change. You must understand Sir that climate change is NOT about just warming. It is about CHANGE which can be either warming or cooling. I repeat. I have always argued that it is in land use changes that the greatest human impacts on climate are to be found. No inconsistency here.

Except, of course, just befre you said that you don’t believe land use changes are a negative feedback.”

My doubts on negative feedback of land use do not change anything about my thoughts on the impact of land use on climate. Land use has a greater regional influence on climate than global (Hansen et. al. 2007).

The feedbacks (actually a climate forcing in Hansen et. 2007) are all related to albedo and roughness. There is no mention in Hansen et. al. 2005; 2007 of dynamic vegetation changes, changes in precipitation patterns due to land use change, influences of fire regimes in land management etc. In fact Hansen et. al. 2005 state “The small land use global climate forcing that we find may not fully represent land use effects, as there are other land use activities, such as irrigation, that we have not included.” They admit that the question of the actual climate forcing of land use change is open to further investigation.

Hansen et. al. 2007 go on further to state: “We exclude land cover changes occurring as a feedback to climate change, except to the extent they are implicitly included in the Ramankutty and Foley (1999) data set.”

and:

“Our subjective estimate is that the global mean land use forcing for 1880–2000 lies between zero and -0.2 W/m2. However, the global value is less relevant than the regional forcing, which can be as much as several W/m2, as shown in Fig. 7 of Efﬁcacy (2005). ”

Note the word subjective used by Hansen et. al. 2007. Their papers regard land use as more of a forcing than a feedback. This would indicate that their knowledge of the overall impacts of land use to climate is limited to those effects that affect albedo, roughness and evapotranspiration changes. I argue that land use changes affect far more than those parameters alone.

It’s interesting (or not) that Richard Steckis several times mentioned land use feedback when he apparently meant land use forcing.

Richard Steckis – while some forcings do have various idiosyncracies in regional affects, there are general tendencies associated with global average warming or cooling, perhaps especially for changes due to forcings such as solar and greenhouse gas changes.

Because:

Regional solar forcing varies by latitude and season and time of day, cloud cover and humidity, ozone…

Feedbacks are not evenly distributed in space and time. Hence temperature will not increase everywhere uniformly or in the same way in every season or for every ENSO index value (also a climate dependent variable in a pattern of fluctuation sense), etc. Convection tends to even out the temperature changes within the troposphere, working against vertical variations in forcing and feedbacks within the troposphere, thus that affects convection. Uneven temperature changes result in change in circulation patterns, humidity and cloud cover distributions, oceanic circulation and salinity, and surface type on land (albedo, soil moisture, vegetation) – which results in changes in temperature, in circulation patterns, humidity and cloud cover distributions, oceanic circulation and salinity, and surface characteristics – etc.

“Land use has a greater regional influence on climate than global (Hansen et. al. 2007).”

Land use having greater regional impact than land use has global impact does not mean that it will have greater regional impact than CO2 forcing.

“They admit that the question of the actual climate forcing of land use change is open to further investigation.”

Sure, but you have to take a big leap from that to the idea that land use overwhelms or even compares to CO2 effects even regionally. Can you build that bridge?

“Hansen et. al. 2007 go on further to state: “We exclude land cover changes occurring as a feedback to climate change, except to the extent they are implicitly included in the Ramankutty and Foley (1999) data set.””

Land cover feedback is not the same as land use, though one can affect the potential of the other.

How CO2 affects land cover and results – well, in so far as CO2 fertilization occurs outside regions with zero runoff, a reduction in evapotranspiration could enhance runoff and result in greater river flow, and perhaps increase the near-surface lapse rate.

“I argue that land use changes affect far more than those parameters alone.”

Effects that are more than those parameters alone can come about through those parameters alone.

Or,

You mean changes in CO2 and CH4 fluxes that result from land use changes? Those are included in the CO2 and CH4 forcing. There can and likely will be CO2 and CH4 feedbacks from climate change, perhaps including through changes in land cover.

Those are actually examples of how a forcing in general might have some idiosyncratic effect, but for solar and greenhouse gas forcing, my understanding is that either they do not vary so much (more so for greenhouse forcing, as solar forcing must vary by latitude, season, and time of day, but the resulting cycles and geographic variations from uneven solar heating do affect greenhouse forcing. For changes from a familiar baseline, both might be a maximum in the subtropics (few clouds, high lapse rate?), though I’m not sure…

But the similar uneven feedbacks generally dominate the idiosyncracies of well-mixed greenhouse gas forcing and solar forcing, so far as I know.

“While the total forcing associated with land use is important, it is also important if different uses of land cause different effects on forcing and have occurred at different times”

Is inaccurace.

It isn’t important.

We know from studies of what happens in the past that temperature sensitivity is between 2 and 4.5C per doubling. Even though the land use change was extraordinary: it went from mostly growing to mostly ice covered. That’s a pretty dramatic land use change.

And for ACCURACY, are the uncertainties cause for complacency or worry?

And for ACCURACY, where is the idea that land use could have had the opposite effect you allude to?

Richard Steckis (354), and Gavin’s inline reply:
Could it be that the confusion arises of which forcing factors are included in “land use”: Clearance of forests causes a negative forcing because of albedo change (forests are generally darker than what it is replaced by), but it has a positive forcing because of CO2 release (which is in the short term partly masked by simultaneous aerosol emissions). Even though a consequence of changes in land use, the latter two are not included in the traditional land use term AFAIK, but rather under GHG and aerosols. Please correct me if I’m wrong.

The main article tlaks about cherrry picking the data to the most recent decade of data on the chart still showing a warming trend. However, if the range of data is taken to start at 2001 through to the present day projected 2009 temperature, there IS a slight cooling trend.
A simple comparison of best-fit simple straight line slopes for all 9-year periods 2001-2009, 2000-2008, 1999-2007 etc shows that the 9-year period until 2009 has the strongest negative slope in the 1980-2009 chart. Negative slopes do also appear for periods after Pinatubo, but the most recent 9 years downward slope is 3 times that of such post-Pinatubo 9-year periods.
But what does this mean?
Aside from the fact that cherry-picking can turn things either way.
Cherry-pick back to 1998, you get warming.
Cherry-pick back to 2001, you get cooling.

Mark, perhaps you would have been better off pointing out to me that not all studies show irrigation as having a warming effect instead of just going off on a tirade. A much better example for my purposes would have been urban sprawl. Regardless, the point is that the land use changes chronology matters.

“And for ACCURACY, are the uncertainties cause for complacency or worry?”

My last comment on this blog for a while since I grow weary of the attacks and eschews. I will decide if the uncertainties are cause for complacency or worry when the warming starts up again, which I agree with you it will. Should this happen before other scientists believe the models have been invalidated then I will consider the models accurate since I can think of no better test then the one they are currently undergoing. Should this happen after other scientists, not just the usual skeptics but scientists such as those at the NOAA, believe the models have been invalidated then I also will believe the models invalidated. Thanks to those of you that have been civil and educational such as, but not inclusive to, Gavin and Martin.

Post 325: 325.Well here is an intersting post that suggests that the main post here is based on cherry-picked data. http://masterresource.org/?p=5240 . It summarizes in an easy to understand manner the data for all major temperature indexes and their trends for a a variety of periods over the last twenty years or so.

[Response: Vaguely ok, but he has failed to take the clear auto-correlation in the monthly data series into account and so his statements about significance are all biased to be over-definitive. – gavin]”

Which explanation of the warming “pause” is more plausible: (1) Simmons hypothesis that there is no pause, it’s just that the Arctic region is under-sampled. Or (2) Hank Robert’s suggestion that the pause is real and it’s a result of polar ice melting? Which effect is stronger?

#383 Hank, I just read the report linked to by dhogaza n #169 and it didn’t discuss the magnitude of the effect of polar ice cubes melting on earth temperature. (But you will understand why I missed this comment when you consider the number of pages to leaf through in these threads.)

Our host Stefan points out that it is “pointless to look for explanations for a warming pause.”

It seems that perhaps the whole discussion about temperature has limited meaning. I assume the surface temperature data is from measurements with a satellite radiometer. The problem is that heat and temperature are not that clearly related, especially in the ocean. One might assume that on average, there is a direct connection. For solid earth that might be true. However, the vertical mixing process along with the vast cold reserves in the ocean makes temperature a poor indicator, and in fact temperature should usually be lower than it would be without that vertical mixing. Simply stated, the heat tends to stay put on solid ground but it can fairly quickly descend, especially if the wind is active. And if heat stimulates weather action, that wind might be produced by the heat and thus made to reduce the surface temperature.

As I see Fig. 2 of the spinnng globe it seems like the ocean is doing a good job of leveling the surface temperature effect of heating due to global warming, except in the arctic. (and it seems there are hotter spots on many of the large land masses) I guess some of the comments here relate to the Arctic ice effects. As I would say it, it looks like the temperature data is unclear here as well. Thick ice can be much colder than the water underneath, but as it thins and disappears the water temperature dominates. The red color coded temperatures of the Arctic seem to be showing the disappearance of the ice. Clearly there would be the heat of fusion (melting in this case) that would represent quite a lot of energy being taken into the ocean due to the global heat imbalance.

So the main point I am trying to make is that the discussion needs to be shifted away from temperature, which is bound to lead to erroneous ideas, some of which would exagerate the problem and some of which would empower those that would deny the problem.

The disappearance of Arctic ice should be strongly noted. Sea level measurements should also get more emphasis.

I have a particular concern for the warming over the north end of Greenland. The several degrees C warming shown here is alarming, subject to some interpretation as to how cold is the base temperature, and whether there is land ice melting or a danger of it going on.

My statement in #391, “Clearly there would be the heat of fusion (melting in this case) that would represent quite a lot of energy being taken into the ocean due to the global heat imbalance,” has to be confusing. I skipped too many steps. I am supposing that deeper ocean regions are warmer than usual due to vertical mixing which ‘takes energy into the ocean and this warmer water is circulating into the Arctic Ocean. This causes sea ice to melt which cools that otherwise warmer water. The Arctic region surface temperature is somewhat indirectly related to this process, since the upper sea ice surface is significantly colder than the water in any case, and when it goes away the water temperature would get measured, at the surface of course. This would show up as the significant warming.

Wouldn’t it be good to have two different names for two kinds of trend?

(a) The populist one based on the slope of a straight line drawn through or between the data points. This comes with no error bars and no estimate of statistical significance.

(b) The same as (a) but with a specified and reasonably large statistical significance or fractional error bars significantly lower than 100%.

Tamino, Grumbine and RC have all discussed this difference which requires no knowledge of climatology or even advanced statistics. Yet it is still the case that type (a) trends crop up all over the place and not only in the recent BBC article mentioned e.g. at #356. Consider e.g.

# 115 Kevin McKinney who says

“A (slight) slowing of the warming”

I could not open your link Kevin, but having read Tamino et al I beg to differ. There is unlikely to be any evidence there either for a slight warming or the opposite because a slight slow down would require several more years to detect. A large slow down might be detectable sooner but there has not been one. We appear to be stuck with the boring but worrying old trend of 0.18K per decade +/- error just as before.

Having written that, I am seriously troubled by Senator Barton’s choice of Wegmann to chair that “impartial” investigation into the original hockey stick papers. According to his recent signing of the Bali letter he appears to be employing trends of type (a). That letter asserted

“Consistent with this, and despite computer projections of temperature rises, there has been no net global warming since 1998.” “

Just spent the afternoon reviewing the new projects to inventory the ice with newer technology and adjust the remote sensors. Study after study show that remote sensors are in need of improvement. Sensor drift provided another flaw this month as well. At this point in time, it would seem that sensor technology is still emerging. Basing an entire world economy on it is not sound science.

I am not so sure that the radiant heat from the sun was not higher in the last few years and lower in conjunction with the absence of sunspots.
The claim that the sun has been cooler for the entire 11 year cycle needs some evidence as well.

It is difficult enough to take accruate readings in small environments. The research presented here on a global scale has a taste of cherry picking the data to support the conclusion. The conclusions with the associated cause and effect are not sound.

Thanks for that correction; sorry about the mistake. I also called Barton a senator instead of a congressman. But I should have gone further than raise the issue of his impartiality. Being partial need not have prevented him from being reliable.